Hypernatraemia and Hyponatraemia Cases

Hypernatraemia

• Hypernatraemia indicates an imbalance of extracellular and intracellular fluid osmolality
• Elevated plasma Na+ creates an osmotic gradient, forcing water out of cells into the extracellular fluid
• The primary cause is usually a dysfunction in the osmoregulatory system
• Understanding effective circulating volume (ECV) regulation helps interpret the underlying cause

Case 1

• A 60-year-old woman found unconscious, likely due to dehydration from a stroke
• Admission vital signs: pulse rate 80/min, blood pressure 140/80, suggestive of dehydration
• Plasma and urine values are provided in a table, showing elevated sodium and osmolality

Case 2

• 56-year-old man with a fractured skull base following a motor vehicle accident experienced a significant fluid loss (5-6 liters)
• Plasma and urine values are provided in a table, illustrating electrolyte imbalances

Hyponatraemia

• Hyponatraemia presents a more complex diagnostic challenge than hypernatraemia
• It can occur without hypo-osmolality, potentially reflecting issues in either osmolality or ECV regulation, or both

Case 3

• A 42-year-old man admitted with acute pancreatitis, displaying a milky blood sample and profound hyponatraemia with normal plasma osmolality
• Plasma and lipid values are provided, revealing the presence of pseudohyponatraemia due to analytical inaccuracies

Pseudohyponatraemia

• This term describes hyponatraemia with normal plasma osmolality due to analytical errors in measuring sodium in the water phase

Dr Damian Griffin

• A Consultant Chemical Pathologist, providing expertise on the diagnosis and interpretation of plasma sodium disturbances

Basis for investigating disturbances of plasma sodium

• Plasma sodium is a surrogate marker for plasma osmolality
• The key regulatory systems are:
  • Osmoregulation
  • Effective circulating volume regulation
• The correlation between plasma sodium and osmolality, and the regulatory responses to sodium disturbances, usually pinpoint the cause of the imbalance

Sodium and Osmolality

• The body primarily regulates osmolality, not sodium
• Measuring osmolality would be ideal, but it is not routinely done due to the lack of widely available automated analytical methods
• Sodium is the major extracellular contributor to osmolality and typically correlates with it, making it a convenient surrogate marker
• During hyponatraemia assessments, it's crucial to consider situations where the normal correlation between sodium and osmolality is disrupted

Osmoregulation

• Controlled by osmoreceptors in the hypothalamus
• Responses to hyperosmolality include:
  • Thirst - regulates water intake
  • Antidiuretic hormone (ADH) secretion - regulates water excretion
• While osmoregulation is a response to plasma osmolality changes, these changes are mainly mediated by water balance fluctuations, not salt balance

Diagram of Osmoregulation

• A diagram depicting the osmoregulatory system, emphasizing the interaction between osmoreceptors, thirst, ADH, and the kidneys

Effective Circulating Volume Regulatory System

• Effective circulating volume (ECV) refers to the rate of capillary circulation perfusion, though it's not quantifiable
• It is maintained by adjusting vascular resistance, cardiac output, and renal sodium and water excretion
• ECV changes are detected by volume receptors in the cardiopulmonary circulation, carotid sinuses, aortic arch, and renal afferent glomerular arterioles
• Responses to ECV changes are primarily through the sympathetic nervous system, angiotensin II generation, and renal Na+ excretion regulation
• In disease, maintaining normal osmolality often takes precedence over specific electrolyte levels
• It’s essential to look for high concentrations of other osmotically active substances (e.g., glucose, urea)

Diagram of Osmoregulation in Case 4

• A diagram showing the osmoregulatory system with values highlighted in red, emphasizing hyponatraemia

Case 5

• A 40-year-old man with schizophrenia exhibited mild confusion, nausea, and vomiting
• The patient reported excessive water consumption (up to 20 liters/day)
• Hyponatraemia with hypotonicity and very dilute urine, suggesting possible syndrome of inappropriate ADH secretion (SIADH)

Diagram of Osmoregulation in Case 5

• A diagram of Osmoregulation with values highlighted in red, emphasizing thirst, water intake, and dilute urine osmolality

Case 6

• A 40-year-old woman experiencing vomiting due to bowel obstruction, appearing dehydrated with an elevated pulse rate and postural hypotension
• Vomit is hypotonic, contributing to potential fluid loss
• Plasma and urine values are provided, illustrating electrolyte imbalances

Diagram of ECV Regulation in Case 6

• A diagram depicting ECV regulation, highlighting the impact of blood pressure on fluid balance

Diagram of Osmoregulation in Case 6

• A diagram of Osmoregulation with values highlighted in red, stressing the augmented ADH secretion and high urine osmolality

Diagram of Osmoregulation in Case 6 - Alternative

• A diagram of Osmoregulation with values highlighted in red, illustrating the presence of increased osmoreceptor stimulation and elevated urine osmolality

Case 7

• A 67-year-old woman with bronchiectasis was admitted with a productive cough and confusion
• Blood pressure was 150/80 mmHg, and the patient was neither clinically volume depleted nor oedematous
• Bilateral widespread coarse crepitations in the lungs, indicating possible pulmonary complications
• Plasma, lipids, and urine values are provided for analysis

Diagram of ECV Regulation in Case 7

• A diagram depicting ECV regulation, emphasizing the potential for discrepancies between clinical presentation and underlying fluid balance

Pseudohyponatraemia (an analytical error!)

• Diagrams highlighting different water and solids content in plasma samples
• Pseudohyponatraemia arises when standard sodium analytical methods fail to account for variations in plasma water volume
• These errors can become more prominent in conditions like hypertriglyceridaemia and hyperproteinemia

Pseudohyponatraemia - How to Pick up on this error

• Two practical approaches can help identify this error:
  • Measure plasma osmolality - provides a direct measure of osmoles per kg of water, a normal osmolality with hyponatraemia suggests pseudohyponatraemia
  • Measure the solids:
    • Total protein
    • Triglycerides - as a marker of elevated lipoproteins

Case 4

• A 14-year-old diabetic presented in a semi-comatose state with a high glucose level (41 mmol/l)
• The patient also displayed hyponatraemia and increased plasma osmolality
• Plasma glucose values are included

Hyponatraemia with hyperosmolality

• This combination indicates that while the patient is hyperosmolar, the excess osmotically active constituent is not sodium
• In healthy individuals, plasma electrolytes, glucose, and urea constitute the primary determinants of plasma osmolality

Explore the critical conditions of hypernatraemia and hyponatraemia through clinical cases. This quiz presents two real-world scenarios that illustrate the effects of sodium imbalance in the body. Understand vital signs, laboratory values, and underlying causes for effective diagnosis.